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Hamilton’s Rule

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Inclusive fitness theory; Kin altruism; Kin selection theory


According to Hamilton’s rule, the cost of an investment must be less than the benefit weighted by the genetic relatedness of the investor and recipient. Based on the condition “all else being equal,” individuals are predicted to invest more in closely genetically related kin compared to more distantly related kin or non-kin.


William D. Hamilton (1964) formulated a rule that defined the conditions under which altruism can evolve and spread in sexually breeding populations. Altruism refers to a behavior that decreases the fitness of the actor while increasing the fitness of another individual (West et al. 2011).

The Rule

Hamilton argued that in addition to the parent–offspring relation, other relatives who share a common descent carry identical copies of the same alleles (Mock 2011). Therefore, individuals can spread their own genes (inclusive fitness) not only by reproducing themselves (direct...

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Correspondence to Hans Hämäläinen .

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Hämäläinen, H., Tanskanen, A.O., Danielsbacka, M. (2018). Hamilton’s Rule. In: Shackelford, T., Weekes-Shackelford, V. (eds) Encyclopedia of Evolutionary Psychological Science. Springer, Cham.

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